1. Field of the Invention
The present invention relates to an aspherical lens which is singly capable of diverging and converging parallel rays of light.
2. Description of the Prior Art
Optical devices for converging parallel rays of light for heating or machining and optical devices for diverging a thin beam of light such as a laser beam have heretofore employed an optical system composed of a plurality of lenses combined together.
FIG. 1(A) of the accompanying drawings illustrates an optical system comprising convex lenses 1, 2 arranged on one central axis and fixedly mounted in a lens housing 3. FIG. 1(B) shows an optical system composed of a convex lens 1 and a concave lens 4 disposed coaxially to each other and fixedly mounted in a lens housing 3. The illustrated optical devices are required to construct the lens housings 3 and assemble the lenses 1, 2, 4 into the lens housings 3 with a high accuracy in order to maintain desired parallelism and concentricity beteen the lenses 1, 2 or the lenses 1, 4. In optical systems using spherical lenses, it is widely practiced to reduce lens aberrations by increasing the number of lenses employed. With such a practice, however, higher accuracy is needed in constructing a lens housing and assembling lenses into the lens housing. Furthermore, since the optical device itself becomes heavy and large in size, any apparatus such as a heating apparatus in which the optical device is incorporated cannot be reduced in physical size. In addition, the loss of light is increased due to reflection on the surfaces of the lenses.
Optical devices may suffer from another problem even if they are constructed with high accuracy. For example, where an incident beam of light 5 as shown in FIG. 1(C) does not coincide with an optical axis 6 of the lens system, a portion of incident light will be trapped in a lens housing 3. With the conventional devices composed of combined lenses, therefore, optical axis adjustment is required to be carried out with considerable care in order to diverge or converge the light efficiently.
As described above, the prior devices for diverging or converging light beams have several problems which essentially accompany optical devices composed of combined lenses. However, a sole lens capable of diverging and converging a beam of light in the same manner as the prior optical devices would not be subjected to the foregoing problems.
Therefore, there has been a demand for a single lens which can diverge and converge a beam of light.